At present, a subscriber initiates a call through a mobile station (MS) or a telephone.
Since there is a personal phone book in a MS, a subscriber can make a call through the phone book; it is convenient, because it does not need to type number keys to make the call. In some cases, a subscriber may have two mobile phones at the same time. For example, when a subscriber is at other city for business, he may rent a local mobile phone at that city for saving money. In this case, usually the rented mobile phone does not have the personal phone book he wants. And when he makes a call, he needs to type in the called phone number, so it is inconvenient to initiate a call with the rented mobile phone.
A telephone is a fixed device; usually several people use the same telephone at different time, such as in an office or at home. It is impossible that every one has a personal phone book in one telephone, this makes a call inconvenient: you have to remember the called phone number and you must type in the called phone number.
On the other hand, using a mobile phone to make a call is a wireless communication; the signal is easily interfered and has some radiation.